Pain is a complex phenomenon that includes a sensory experience that usually involves an awareness of a noxious stimulus or bodily harm. Individuals experience pain through diverse causes, from various daily hurts and aches, through more serious injuries or illnesses.
Despite its unpleasantness, pain is an important part of the existence of humans and other animals; in fact, it is vital to healthy survival. Pain is part of the body's defense system, triggering mental and physical behavior to end the painful experience. It promotes learning so that repetition of the painful situation will be less likely. Pain encourages an organism to disengage from the noxious stimulus associated with the pain. Preliminary pain can serve to indicate that an injury is imminent, such as the ache from a soon-to-be-broken bone. Pain may also promote the healing process, since most organisms will protect an injured region in order to avoid further pain.
A plethora of molecular mediators have been implicated in pain perception, including sodium, potassium and calcium ion channels. A huge diversity of analgesic drugs are in use today. Examples include non-steroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, narcotic drugs such as morphine, synthetic drugs with narcotic properties such as tramadol, and various others.